NF3 is employed, for example, as a gas for dry etching or a gas for cleaning or the like in a manufacturing process of a semiconductor device. In general, the production methods of this gas are roughly classified into chemical methods and electrolytic methods. Known chemical methods include a method (1) in which F2 gas and NH3 gas are injected into a fused acidic ammonium fluoride (see Japanese Patent Application Publication No. S55-8926 (Patent Document 1)), and a method (2) in which an F2 gas is directly reacted with an NH3 gas (see Japanese Patent Laid-Open Publication No. H02-255513 (Patent Document 2) and Japanese Patent Laid-Open Publication No. H05-105411 (Patent Document 3)).
On the other hand, known electrolytic methods are, for example, a method (3) in which the electrolyzation is carried out by using a fused acidic ammonium fluoride as an electrolyte and graphite as an anode, and a method (4) in which the electrolyzation is carried out by using a fused acidic ammonium fluoride as an electrolyte and nickel as an anode. In addition, Ruff et al. have reported that an F2 gas is reacted with an NH3 gas in a gaseous phase to chemically synthesize NF3 with a yield of 6% or less (see Z. anorg. allg. chem. 197, 395 (1931) (Non-Patent Document 1)). Morrow et al. have also reported that NF3 is synthesized in a gaseous phase in the same manner with a yield of 24.3% (see J. Amer. Chem. Soc. 82. 5301 (1960) (Non-Patent Document 2)).
Since an extremely reactive F2 gas is used in the conventional direct fluorination reactions in which an F2 gas is reacted with NH3 to synthesize NF3, there has been a problem that there is danger of explosion and corrosion. Further, the temperature inside a reactor increases because these reactions generate a large amount of heat, which fact leads to the decrease of the yield due to the generation of N2, HF, N2F2, N2O, NH4F (ammonium fluoride), NH4HF2 (acidic ammonium fluoride) and the like by side reaction and the decomposition and side reaction of NF3, and which fact also results in the clogging of the reactor and pipes with solids of NH4F and NH4HF2.
Among these problems, Japanese Patent Laid-Open Publication No. H02-255511 (Patent Document 4) and Japanese Patent Laid-Open Publication No. H02-255512 (Patent Document 5) describe that the clogging of a reactor and pipes is improved by using a thin and rectangular-shaped reactor which has an ammonia gas injection tube on an upper side and a fluorine gas injection tube on a side, or by placing a reactor in a heating medium bath maintained at 80 to 250° C. However, both methods have a low yield of approximately 17% (on the basis of NH3). In addition, Japanese Patent Laid-Open Publication No. H02-255513 (Patent Document 2) describes that the yield is increased to 59.5% (on the basis of NH3) by using 3 to 20 times as much an F2 gas as an NH3 gas, but the yield is poor on the basis of F2 and this method is not economical.
Japanese Patent Laid-Open Publication No. H05-105411 (Patent Document 3) describes that no clogging of a reactor and pipes occurs and the yield is improved to 63% (on the basis of NH3) by spirally flowing raw material gases along the inner wall of a reactor to mix and react the raw material gases in the reactor. However, since an expensive F2 gas is used, the problem is to further increase the yield.
Japanese Patent Laid-Open Publication No. 2001-322806 (Patent Document 6) describes that the yield is improved to approximately 76% (on the basis of F2) by conducting the reaction at 80° C. or lower in the presence of a diluting gas, but there is a problem with the clogging of a reactor and the yield improvement.
[Patent Document 1] Japanese Patent Application Publication No. S55-8926
[Patent Document 2] Japanese Patent Laid-Open Publication No. H02-255513
[Patent Document 3] Japanese Patent Laid-Open Publication No. H05-105411
[Patent Document 4] Japanese Patent Laid-Open Publication No. H02-255511
[Patent Document 5] Japanese Patent Laid-Open Publication No. H02-255512
[Patent Document 6] Japanese Patent Laid-Open Publication No. 2001-322806
[Non-Patent Document 1] Z. anorg. allg. chem. 197, 395 (1931)
[Non-Patent Document 2] J. Amer. Chem. Soc. 82. 5301 (1960)